Aqueous Persistent Noncovalent Ion-Pair Cooperative Coupling in a Ruthenium Cobaltabis(dicarbollide) System as a Highly Efficient Photoredox Oxidation Catalyst

Abstract

An original cooperative photoredox catalytic system, [RuII(trpy)­(bpy)­(H2O)]­[3,3′-Co­(1,2-C2B9H11)2]2 (C4; trpy = terpyridine and bpy = bipyridine), has been synthesized. In this system, the photoredox metallacarborane catalyst [3,3′-Co­(1,2-C2B9H11)2]− ([1]− ) and the oxidation catalyst [RuII(trpy)­(bpy)­(H2O)]2+ (C2′) are linked by noncovalent interactions and not through covalent bonds. The noncovalent interactions to a large degree persist even after water dissolution. This represents a step ahead in cooperativity avoiding costly covalent bonding. Recrystallization of C4 in acetonitrile leads to the substitution of water by the acetonitrile ligand and the formation of complex [RuII(trpy)­(bpy)­(CH3CN)]­[3,3′-Co­(1,2-C2B9H11)2]2 (C5), structurally characterized. A significant electronic coupling between C2′ and [1]− was first sensed in electrochemical studies in water. The CoIV/III redox couple in water differed by 170 mV when [1]− had Na+ as a cation versus when the ruthenium complex was the cation. This cooperative system leads to an efficient catalyst for the photooxidation of alcohols in water, through a proton-coupled electron-transfer process. We have highlighted the capacity of C4 to perform as an excellent cooperative photoredox catalyst in the photooxidation of alcohols in water at room temperature under UV irradiation, using 0.005 mol % catalyst. A high turnover number (TON = 20000) has been observed. The hybrid system C4 displays a better catalytic performance than the separated mixtures of C2′ and Na­[1], with the same concentrations and ratios of Ru/Co, proving the history relevance of the photocatalyst. Cooperative systems with this type of interaction have not been described and represent a step forward in getting cooperativity avoiding costly covalent bonding. A possible mechanism has been proposed.

Molecular and supported ruthenium complexes as photoredox oxidation catalysts in water

“…Few examples involving only a photocatalyst have been carried out. [16][17][18][19][20] The most studied ruthenium complexes have been [Ru(bpy) 3 ] 2+ 21,22 and derivatives 23,24 as photocatalysts; however, very few ruthenium aqua complexes have been tested both as a photosensitizer and a catalyst in the oxidation of organic substrates in water. 25 From the perspective of sustainability and industrial applicability, the grafting of homogeneous catalysts on solid supports with a high surface is a good approach.…”

“…Few examples involving only a photocatalyst have been carried out. 16–20 The most studied ruthenium complexes have been [Ru(bpy) 3 ] 2+ 21,22 and derivatives 23,24 as photocatalysts; however, very few ruthenium aqua complexes have been tested both as a photosensitizer and a catalyst in the oxidation of organic substrates in water. 25…”

Light‐Induced On/Off Switching of the Surfactant Character of the o‐Cobaltabis(dicarbollide) Anion with No Covalent Bond Alteration

“… [2] In the last decades, a vast number of studies have described its physical and chemical properties, highlighting its thermal and chemical stability, most probably due to its strong aromatic character. [2] These and other properties, in conjunction with its facile synthesis [3] and derivatization, [2] make this molecule highly attractive for the development of multiple applications in a plethora of fields,[ 4 , 5 ] including catalysis,[ 6 , 7 ] redox chemistry, [8] (bio)sensors,[ 9 , 10 , 11 ] medicine,[ 5 , 12 , 13 , 14 , 15 , 16 ] metal‐organic frameworks, [17] conducting polymers,[ 18 , 19 ] and surfactants,[ 20 , 21 ] among others. [ 5 , 22 ]…”

A stand-alone cobalt bis(dicarbollide) photoredox catalyst epoxidates alkenes in water at extremely low catalyst load

“…Recently, we have shown that Na [1], and its chloro derivatives, act both as catalyst and photosensitizer, being highly efficient in the photooxidation of alcohols in water, through single electron transfer processes (SET), 58 and via proton-coupled electron transfer (PCET). 59 High performance of Na [1] in the photooxidation of alcohols is observed, using catalyst load to 0.01 mol % and reaching TON= 10000, in some cases. We have also supported the metallabis(dicarbollide) catalyst on silica-coated magnetite nanoparticles.…”